Significant amount of attention has been placed on developing new technologies for providing energy from resources other than fossil fuels. Biomass is a resource that shows promise as a fossil fuel alternative. As opposed to fossil fuel, biomass is also renewable.
One type of biomass is plant biomass. Plant biomass is the most abundant source of carbohydrate in the world due to the lignocellulosic materials in its cell walls. Plant cell walls are divided into two sections, primary cell walls and secondary cell walls. The primary cell wall provides structure for expanding cells and is composed of major polysaccharides (cellulose, pectin, and hemicellulose) and glycoproteins. The secondary cell wall, which is produced after the cell has finished growing, also contains polysaccharides and is strengthened through polymeric lignin covalently cross-linked to hemicellulose. Cellulose includes high molecular weight polymers formed of tightly linked glucose monomers, while hemicellulose includes shorter polymers formed of various sugars. Lignin includes phenylpropanoic acid moieties polymerized in a complex three dimensional structure. Overall, the composition of the lignocellulosic biomass is roughly 40-50% cellulose, 20-25% hemicellulose, and 25-35% lignin, by weight percent.
Most transportation vehicles, whether boats, trains, planes and automobiles, require high power density provided by internal combustion and/or propulsion engines. These engines require clean burning fuels which are generally in liquid form or, to a lesser extent, compressed gases. Liquid fuels are more portable due to their high energy density and their ability to be pumped, which makes handling easier. This is why most fuels are liquids.
Currently, biomass provides the only renewable alternative for liquid transportation fuel. Unlike nuclear and wind applications, and for the most part solar resources, biomass is capable of being converted into a liquid form. Unfortunately, the progress in developing new technologies for producing liquid biofuels has been slow, especially for liquid fuel products appropriate for jet, diesel and heavy fuel oil applications. Although a variety of jet and diesel fuels can be produced from biomass resources, such as biodiesel, Fischer-Tropsch diesel, and jatropha and palm oil jet fuels, these fuels are often limited in their use due to their respective characteristics. The production of these fuels also tends to be expensive and raises questions with respect to net carbon savings.
Biodiesel, for example, can be made from vegetable oil, animal fats, waste vegetable oils, microalgae oils or recycled restaurant greases, and is produced through a process in which organically derived oils are combined with alcohol (ethanol or methanol) in the presence of a catalyst to form ethyl or methyl esters. The biomass-derived ethyl or methyl esters can then be blended with conventional diesel fuel or used as a neat fuel (100% biodiesel). Biodiesel is also expensive to manufacture, and poses various issues in its use and combustion. For example, biodiesel is not suitable for use in lower temperatures and requires special handling to avoid gelling in cold temperatures. Biodiesel also tends to provide higher nitrogen oxide emissions and cannot be transported in petroleum pipelines.
Biomass can also be gasified to produce a synthesis gas composed primarily of hydrogen and carbon monoxide, also called syngas or biosyngas. Syngas produced today is used directly to generate heat and power, but several types of biofuels may be derived from syngas. Hydrogen can be recovered from syngas, or the syngas can be catalytically converted to methanol. Using Fischer-Tropsch catalysts, the gas can also be converted into a liquid stream with properties similar to diesel fuel. These processes are energy and capital intensive, and are limited by the availability of biomass at volumes appropriate for the scale needed to be commercially effective.
The above technologies are also inefficient and either fail to make use of the plant's carbohydrate material or require the total destruction and reassembly of its carbon backbone. Bioreforming processes have recently been developed to overcome these issues and provide liquid fuels and chemicals derived from the cellulose, hemicellulose and lignin found in plant cell walls. For instance, cellulose and hemicellulose can be used as feedstock for various bioreforming processes, including aqueous phase reforming (APR) and hydrodeoxygenation (HDO)—catalytic reforming processes that, when integrated with hydrogenation, can convert cellulose and hemicellulose into hydrogen and hydrocarbons, including liquid fuels and other chemical products. APR and HDO methods and techniques are described in U.S. Pat. Nos. 6,699,457; 6,964,757; 6,964,758; and 7,618,612 (all to Cortright et al., and entitled “Low-Temperature Hydrogen Production from Oxygenated Hydrocarbons”); U.S. Pat. No. 6,953,873 (to Cortright et al., and entitled “Low-Temperature Hydrocarbon Production from Oxygenated Hydrocarbons”); and U.S. Pat. Nos. 7,767,867 and 7,989,664 and U.S. Application No. 2011/0306804 (all to Cortright, and entitled “Methods and Systems for Generating Polyols”). Various APR and HDO methods and techniques are described in U.S. Pat. Nos. 8,053,615; 8,017,818 and 7,977,517 and U.S. patent application Ser. Nos. 13/163,439; 13/171,715; 13/163,142 and 13/157,247 (all to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); U.S. Patent Application No. 2009/0211942 (to Cortright, and entitled “Catalysts and Methods for Reforming Oxygenated Compounds”); U.S. Patent Application No. 2010/0076233 (to Cortright et al., and entitled “Synthesis of Liquid Fuels from Biomass”); International Patent Application No. PCT/US2008/056330 (to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); and commonly owned co-pending International Patent Application No. PCT/US2006/048030 (to Cortright et al., and entitled “Catalyst and Methods for Reforming Oxygenated Compounds”), all of which are incorporated herein by reference. Additional techniques for converting cellulose, hemicellulose and lignin to useable feedstocks for the above APR and HDO processes are described in U.S. patent application Ser. No. 13/339,720 (to Qiao et al., and entitled “Solvolysis of Biomass Using Solvent from a Bioforming Process”); U.S. patent application Ser. No. 13/339,661 (to Qiao et al., and entitled “Organo-Catalytic Biomass Deconstruction”); U.S. patent application Ser. No. 13/339,553 (to Qiao et al., and entitled “Catalytic Biomass Deconstruction”); and U.S. patent application Ser. No. 13/339,994 (to Qiao et al., and entitled “Reductive Biomass Liquefaction”).
One of the keys to commercializing the above technologies is to further refine the processes to maximize product yield and extend catalyst lifetime. Also of interest is the ability to tailor the reactions to produce specific products of high demand or of higher commercial value. Accordingly, what is needed is a more refined process for converting biomass and biomass-derived feedstocks to a greater quantity of heavier hydrocarbons useful in jet and diesel fuels, or as heavy oils for lubricant and/or fuel oil applications.